1. Field of the Invention
The present invention relates to a write head which has a recessed stitched yoke on a planar portion of a zero throat height (ZTH) defining insulation layer and more particularly to a write head which has first and second components, the first component extending from an air bearing surface (ABS) to form a pole tip and a second component recessed and connected to the first component over a flat portion of a first insulation layer that defines ZTH.
2. Description of the Related Art
An inductive write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The second pole piece layer has a pole tip portion which extends from the ABS to a flare point and a yoke portion which extends from the flare point to the back gap. The flare point is where the second pole piece begins to widen (flare) to form the yoke. The placement of the flare point directly affects the magnitude of the write field seen at the recording medium. Since the magnetic flux decays as it travels down the length of the second pole tip, more flux will reach the recording media if the length of the second pole tip is made short. Therefore, optimal performance can be achieved by aggressively placing the flare point close to the ABS so that the second pole tip is made short.
Another parameter important to the design of the write head is the location of the zero throat height (ZTH). Zero throat height is the location where the first and second pole pieces first separate from one another after the ABS. The ZTH separation is caused by the contour of an insulation layer, typically the first insulation layer in the insulation stack. Flux leakage between the first and second pole pieces is further minimized by locating the ZTH as close as possible to the ABS. Also, sloping sides further hinders post processing steps such as ion milling.
Unfortunately, the aforementioned design parameters present a dilemma in the fabrication of the second pole tip. The second pole tip should be well-defined in order to produce well-defined written tracks on the rotating disk. Poor definition of the second pole tip may result in overwriting of adjacent tracks. A well-defined second pole tip should have parallel planar side walls which are perpendicular to the horizontal plane of the first pole piece layer. In most write heads the second pole tip is formed along with the yoke after the formation of the first insulation layer, the coil layer and the second and third insulation layers. Each insulation layer includes a hard-baked photoresist having a sloping front surface.
The sloping surface defines an apex angle which rises from a plane normal to the ABS. After construction, the first, second and third insulation layers present sloping surfaces which face the ABS. The sloping surfaces of the hard-bake resist exhibit a high optical reflectivity. When the second pole tip and yoke are constructed, a thick layer of photoresist is spun on top of the insulation layers and photo patterned to shape the second pole tip, using the conventional photo-lithography technique. In the photo-lithography step an exposing beam, such as light, is directed vertically through slits in an opaque mask, exposing areas of the photoresist which are to be removed by a subsequent development step. One of the areas to be removed is the area where the second pole piece (pole tip and yoke) are to be formed by plating. Unfortunately, when the location of the flare point is placed on the sloping surfaces of the insulation layers ultraviolet light will be reflected forward toward the ABS into photoresist areas at the sides of the second pole tip area. After developing, the side walls of the photoresist are cut which causes the pole tip to be poorly formed after plating. This is called "reflective notching". As stated hereinabove this causes overwriting of adjacent tracks on a rotating disk. It should be evident that, if the flare point is recessed far enough into the head, the effect of reflective notching would be reduced or eliminated since it would occur behind the sloping surfaces. However, this solution produces a long second pole tip which quickly degrades the head's ability to effectively write on the recording medium.
Future high density recording will require heads with first and second pole tips that have side walls that are vertically aligned. Such structures provide superior on track and track edge writing characteristics at high linear and high track densities. Ion milling techniques are typically used to fabricate such write head structures. In this process the first pole is milled into using the second pole tip as a mask. Automatic alignment of the first and second pole tip is achieved since the second pole tip is used as the milling mask to protect the region of the first pole tip that is directly beneath it while the unprotected P1 material on either side of the second pole tip P2 is removed by the milling process. The effect of this milling process forms a "notched P1" structure which has the aligned vertical side walls between P1 and P2. Unfortunately, when the second pole tip is poorly formed, the notches in the first pole piece are poorly formed.
In order to overcome the aforementioned reflective notching and P1 notching problems some second pole pieces are constructed from two or more components wherein a first component forms the second pole tip. The first component is constructed before the insulation layers to eliminate the reflective notching problem. After forming the first pole piece layer and the write gap layer, a photoresist layer is spun on the partially completed head. The photoresist layer is very flat so that ultraviolet light from the photo-patterning step is not reflected forward. After construction of the first insulation layer, the coil layer and the second and third insulation layers, the second component of the second pole piece is stitched to the first component at the ABS, and extends from the ABS to the back gap. Since the second pole tip is well-formed, well-formed notches can be made in the first pole piece.
Another problem with this head is that the ZTH is dependent upon the location of the recessed end of the first component. Since the first component has to be long enough to provide a sufficient stitching area, this length may result in undesirable flux leakage between the first and second pole pieces. Therefore, a small real estate is available to stitch the second component to the first pole piece component. This causes the second pole piece component to extend out into the ABS. Since the second component of the pole piece is typically wider than the first component of the pole piece, viewed from the ABS, the second pole piece has a T-shape. The upright portion of the T is the front edge of the first component of the second pole piece, and the cross of the T is the front edge of the second component. A problem with this configuration is observed during operation when flux fringes from the outer corners of the second component of the pole piece T, to the first pole piece, which can cause adjacent tracks to be overwritten.
Accordingly, there is a strong felt need to provide an inductive write head wherein definition of the side walls of the second pole tip is substantially unaffected by the locations of the flare point and the ZTH.